Vapor generating and superheating system



F3127, 1968 P, E. KURRL E 3,370,572.

VAPOR GENERATING AND SUPERHEATING SYSTEM Filed Sept. '29, 1966 sSheets-Sheet 1 1 M M wt INVENTOR.

Paul E. Kur rle Feb. 27, 1968 KURRLE 3,370,572

VAPOR GENERATING AND SUPERHEATING SYSTEM Filed Sept. '29, 1966 v 3Sheets-Sheet 2 I i l 53 f v 91 I 5 4 r 55 w '1 3 71 7/0 3 l I 9 as Feb.27, 1968 P. E. KLAJFERLE 3,370, 7

VAPOR GENERATING AND SUPERHEATING SYSTEM Filed Sept. 29, 1966 3Sheets-Sheet 3 PEAK STEAM FLOW 3o (I I E 3 o J V LL -ACCUMULATORDISCHARGE W 7 7 "7 7 J 9 1o '20 3o 40 5o FBLOWING o TAP AND CHARGE NExT18 MINUTES 30 MINUTES CYCLE United States Patent tion of New JerseyFiled Sept. 29, 1966, Ser. No. 583,038 9 Claims. (Cl. 122-7) The presentinvention relates to vapor generating and superheating apparatus, andmore particularly to apparatus wherein steam produced in the course of acyclic exothermic process is combined with steam from a separately firedpower boiler to provide a steam power source of substantially constantflow rate at uniform temperature and pressure.

The production of steel in a basic oxygen furnace is an example of sucha process. Here the hot gases emitted from the furnace are passedthrough a water cooled conduit or hood wherein and whereby the gases arecooled, the water cooled conduit walls absorb heat from the gases andthereby generate steam. The operation of the oxygen furnace is cyclic innature since the introduction of the oxygen to initiate the refiningoperation is but of relatively short duration with respect to the totalelapsed time for one cycle. Moreover the rate of steam generationclosely follows the heat release pattern of the furnace cycle, withmaximum generation occurring during the period of oxygen flowing. Thesteam produced in the hood has sometimes been condensed by heat exchangewith other fluids and recycled to the walls of the hood without anyattempt to benefically recover the heat absorbed from the hot furnacegases. Some installations have attempted to use the steam produced inthe hoods by passing the cyclically produced steam to accumulators andthen flashing it to some lower pressure so that a generally uniform flowof saturated steam, from the accumulator, will result. The steam sodischarged may be utilized for various steel plant purposes but it ishighly desirable to increase the usefulness of such steam bysuperheating.

In the present invention a separately fired power boiler served by highheat value fuel is utilized to generate saturated steam, or evenslightly superheated steam, and the steam so produced is mixed withsaturated steam from an accumulator and then passed through asuperheater disposed in a gas pass receiving gases from the powerboiler, where the mixture may be superheated to the desired degree. Thefinal superheat temperature of the steam may be controlled by the firingrate of the power boiler and by fiow regulation of the power boilergases passing over the superheater serving the steam mixture. With thisarrangement it has been found possible to adequately control both thequantity and the superheat temperature of the combined steam flowsproduced in the installation to provide a substantially uniform steamsuperheat temperature leaving the superheater.

Of the drawings:

FIG. 1 is a diagrammatic flow sheet showing the equipment arrangement ofthe present invention;

FIG. 2 is an enlarged elevation, in section, of a portion of theapparatus shown in FIG. 1;

FIG. 3 is a plan View, in section, taken on the line 3-3 of FIG. 2; and

FIG. 4 is a diagram illustrative of steam production and accumulatordischarge rates from an oxygen furnace hood.

In the embodiment of the invention illustrated in the drawings, steamproduced by the hot gases cyclically discharged from a basic oxygenfurnace is discharged at a relatively high pressure to an accumulator sothat a uniform quantity of relatively low pressure saturated steam willbe available for external use. The steam from 3,370,572 Patented Feb.27, 1968 the accumulator is mixed with steam produced in a power boiler,where the mixture of accumulator steam and power boiler steam is passedthrough a super-heater provided with heat from the gases of combustionproduced in the power boiler. As hereinafter described, the operationsof the power boiler are regulated to permit a substantially uniformtemperature and pressure in the mixed superheated steam discharged fromthe superheater.

Referring particularly to FIG. 1, two oxygen furnaces 10 and 11 areillustrated, where in general only one furnace is operated at a time. Inthe usual operation of a plant of this type one furnace is operatedwhile the other furnace is being repaired although under some conditionsboth furnaces may be simultaneously operated for a short period of time.It will be further understood that more than two furnaces may beconnected into the system without changing the basic arrangement ofapparatus or its mode of operation.

With one of the furnaces in operation (for example, furnace 10) the hotgases discharged from the furnace during the oxygen refining period aredischarged through a fluid cooled hood 12 of the general type disclosed,for example, in U.S. Patent 3,168,073. In hoods of this type acontinuous stream of high pressure water is discharged by a pump 13 toinlet headers 14 adjacent the lower end of the hood to flow in parallelthrough tubular elements lining the walls of the hood and discharge as asteam and water mixture to outlet headers 15 from which the mixture isdischarged to a steam and water drum 16.

The drum 16 is provided with the usual blow down connections, vents andsafety valves (not shown) and with makeup water supplied through avalved inlet pipe 17 which receives water from a feed water pump 18. Thedrum 16 is provided with a water level control of conventional type. Inthe drum the steam and water discharged from the riser tubes 20 isseparated, with the water combined with makeup water being dischargedthrough a downcomer 21 to the pump 13. The separated steam dischargesfrom the drum 16 through a valved conduit 22 which joins a correspondingconduit 23 from a corresponding vapor generating unit 24 associated withthe basic oxygen furnace 11. The steam from either or both of the steamgenerating units of the furnaces 10 and 11 is discharged through a line25 to an accumulator tank 26.

The accumulator tank 26 is sized to receive the steam produced in eitheror both of the steam generating units of the basic oxygen furnaces.Suitable quantities of makeup water are supplied to and excess waterremoved from the accumulator tank through pipe 27 so that the steamdischarged thereto through valved pipe 28 is condensed and stored for acontinuous, substantially uniform discharge of lower pressure steamthrough the valved pipe 30 opening to the upper side of the accumulatortank. Suitable pressure reducing and flow control valves are providedfor regulation of the high pressure water which is flashed to steam inleaving the accumulator. As shown, the high pressure steam inlet pipe 28to and the relatively low pressure outlet pipe 30 from the accumulatorare interconnected by a conduit 31 which is provided with a check valve32 for pressure regulation between the inlet and outlet pipes. The lowpressure saturated steam discharged from the accumulator is passedthrough pipe 30 and a suitable cut off valve 33 for delivery to a mixingT 34.

The mixing T receives saturated steam from the accumulator and inaddition also receives steam from a power boiler 35. It will beunderstood the steam from the power boiler may be saturated orsuperheated depending upon the overall heat requirements of the system.The steam from the accumulator 26 and from the power boiler will be atsubstantially the same pressure, are mixed in the mixing T and deliveredthrough a pipe 37 to the inlet header 36 of a superheater 38 associatedwith the .power boiler. The steam is superheated for discharge throughan outlet header 40 and through a pipe 41 which is connected to thesteam main (not shown) of the plant in which the basic oxygen furnacesare installed. The power boiler 35 is provided with a feed water pump 42for delivery of feed Water to the power boiler to com- 'pensate for thesteam discharged therefrom. In the usual installation, a common hot wellwill supply makeup water to the oxygen furnace hoods and the powerboiler.

The operation of a basic oxygen furnace for the refining of steel iswell known and while the exact cycle of operation will vary from plantto plant a typical cycle is illustrated in FIG. 4. As shown in thisfigure, the blowing time during which oxygen is injected into thefurnace will average about 18 minutes while the tap and charge periodwill approximate 30 minutes. Thus each cycle will be completed in aperiod of approximately 48 minutes. During the blowing period the steamdischarged from the hood such as shown in FIG. 1 will reach a peak ina'matter of minutes and then decline to a substantially zero steamproduction at the end of the blowing :period. During the steamproduction period, in the illustrated example, approximately 300,000pounds of steam .per hour will be supplied for a period of time measuredin one or two minutes.

As also indicated on FIG. 4 the accumulator 26 of FIG. 1 Will be sizedand controlled to discharge a substantially uniform fiow of steamtherefrom. In the illustrated example of FIG. 4 the steam discharge willbe of the order of 50,000 pounds of steam per hour. It will beunderstood that in the ordinary operation of a basic oxygen furnace 'theamount of steam produced in each cycle of iron refining will vary andthus the the total amountof steam available in the accumulator will alsovary and fora uniform availability of steam to a steam main -it isdesirable to arrange the power boiler so it can compensate for"relatively limited variations in theavailability of steam from theaccumulator. As hereinafter described, the power boiler is constructedand arranged to permit a limited change in its vapor generating rate andalso to permit a controllable variation in both the temperatureandweight of gases'passed through the superheater. With this arrangementthe combination of steam from the accumulator and from the power boilercan be regulated to produce a substantially uniform quantity ofsuperheated steam discharged from the superheater outlet header wherethe steam may also be controlled for a substantially uniform superheatedtemperature and pressure.

The power boiler 34 and superheater 38 of FIG. 1 are shown in detail inFIGS. 2 and 3. The boiler includes an upper steam and water drum 51 anda lower water drum 52 interconnected by a bank 53 of vapor generatingtubes. A furnace chamber 54 is positoned on one side of the tube bank53, with the walls of the furnace lined by vapor generating tubes '55opening to the drums 51 and 52. The furnace is provided with aconventional "high heat valuefuel burner 56 in a-port 57 in one wall'58for the supply of fuel to the furnace to produce hot gases ofcombustion. The gases of combustion move through the furnace 54 betweena side wall 60 and a bafile wall '61 toward the rear wall 62 todischarge through a gas outlet 63 formed between the rear wall and theend of the bafile wall 61. As shown, the convection tube bank 53 endsadjacent the end of the baflle wall '61, and a gas outlet 64 is formedin the side wall 65 leading directly into the superheater 38. A secondgas outlet 66 is formed inthe opposite end'of the wall 65, so that theflow of gases leaving the furnace 54 can pass to both 'of the gasoutlets 6 4 and 66, or either, as regulated by dampers hereinafterdescribed. With this construction the proportions of gas flow throughthe superheater and through the vapor generating bank 53 can becontrolled for superheat temperature regulation.

The boiler may be provided with a bank of superheater tubes 67 betweenthe gas outlets 63 and 64 and between the rear row 68 of tubes in thebank 53 and the wall 62. (See FIG. 3.) Under these circumstances thesteam from the drum 51 will pass through the superheater to the mixing T34. When the superheater '67 is omitted the flow of steam from the drum51 will pass directly through pipe 70 to the mixing T 34, as shown inFIG. 2.

The superheater 38 is formed with ceramic refractory Walls, with theroof 67, rear wall 68 and floor 70' cooled by a row of tubes 71connecting the superheater inlet header 36 with a steam distributingheader 72. The superheater housing is provided with a longitudinalbafile 73 which extends the full height of the superheater housing andprojects from a position adjoining the gas outlet 64 to an end position74 spaced from the rear wall 68 of the superheater housing. With thisarrangement, heating gas flow entering the superheater housing from theoutlet 64 passes lengthwise along one side of the superheater andreverses its flow direction around the end position 74 to flow throughan outlet 75 formed in a side wall 76 of the superheater housing. A duct77 connects the outlet 75 with a second duct 78 which interconnects theconvection gas pass outlet 66 with an induced draft fan 80. The powerboiler may be pressurized, omitting the fan 80, with the combined gasesfrom duct 78 discharged directly to a stack. The gas ducts 77 and 78 areprovided with dampers S1 and 82, respectively, so that the flow from thevapor generator 35 (FIG. 1) can be regulated with controllableproportioning through the superheater and through the vapor generatingsection of the boiler.

A shown particularly. in FIG. 2, the steam passing from the accumulatorshown in FIG. 1 flows through its discharge duct 30 to the mixing T 34where the accumulator steam is combined with a flow of steam originatingthe upper steam and water drum 51 of the power boiler. The mixture ofsteam discharging through the pipe opens to the inlet header 36 of thesuperheater. Thereafter the steam passes through the row of tubes 71 tothe header 72, as hereinbefore described, for discharge through tubes 83to the steam inlet end portion 84 of the steam outlet header 40. Each ofthe headers ,gas flow through the gas pass 91 defined by wall 76 andbafiie 73. The steam entering the header 88 passes through theinterconnecting tubes in succession through the headers 87, 86 and 85for discharge into the dis-' charge header 40.

It will be noted in the diagram of FIG. 4, the accumulator discharge ofsaturated steam represents a flow of approximately 49,000 pounds ofsteam per hour. Under these conditions the power boiler may be operatedto produce approximately 12,000 pounds of steam per hour. It is ofcourse understood that the accumulator 26 will be regulated by knownvalve controls to discharge steam at a generally uniform rate therefromat a pressure which is maintained substantially uniform. The pressurefrom the accumulator is selected so that the pressure of the steamentering the mixing T 34 from the accumulator will be substantiallyequal to the steam pressure entering'the mixing T 34 from the power:boiler. It is known in the use of an accumulator that under theconditions described in connection with FIG. 21, the hood will beoperated at a pressure of the order of 600 pounds per square inchabsolute (p.s.i.a. so that the stored'steam'in the accumulator may bedischarged therefrom at a pressure, for example of 200 p.s.i.a. Withthis construction the supply of steam will be continuous at'the-pressureselected, :and'if for'any reasonthe steam added to the accumulatorduring the blowing cycle of the oxygen furnace is not adequate toprovide for a uniform discharge of 49,000 pounds of steam per hour fromthe accumulator, the difference between the accumulator discharge andthe desired flow rate of the steam mixtrue can be compensated for byincreasing the steam generation of the power boiler. This can be acomplished without adverse afiect upon the total superheat temperatureof the mixture discharged from the header 40 by increasing the firingrate to the power boiler. Such an increase will permit an increase inthe flow of gases over the vapor generating portion of the power boilerwhile still maintaining adequate gas flow rates and gas temperaturethrough the superheater to maintain superheat temperatures in themixture discharged.

In controlling the apparatus shown in FIGS. 2 and 3 the basic controlwill be a proportioning control device indicated at 93 positioning thedampers 81 and 82 in response to the temperature of the steam dischargedfrom the header 40, as determined by a temperature sensor 94. The supplyof fuel to the burner 56 may also be regulated in known manner inaccordance with the steam flow and temperature conditions prevailing inthe steam outlet 40.

What is claimed is:

1. A steam generating and superheating system'ineluding a power boiler,said power boiler comprising a furnance, means for burning high heatvalue fuel in said furnace, a convection gas-pass divided into a pair ofparallel gas flow sections communicating with said furnace, a bank ofsteam generating tubes positioned in one of said sections, a bank ofsteam superheating tubes in the other of said sections, means forproportioning gas flow from said furnace to said parallel gas flowsections, a steam accumulator, mixer means for combining a flow ofsaturated steam from said accumulator and steam from said steamgenerator for delivery of the mixture to said superheater tubes, andmeans responsive to the temperature of the mixed superheated steamleaving said superheater tubes to proportion gas flow through saidparallel gas flow sections.

2. A steam generating and superheating system according to claim 1wherein means provide a substantially uniform flow of saturated steam ata substantially uniform pressure from said accumulator.

3. A steam generating and superheating system according to claim 1wherein steam generating means supply said accumulator with saturatedsteam at a cyclic rate of flow.

4. A steam generating and superheating system according to claim 3wherein said accumulator steam supply means includes a water cooled hoodserved by a cyclic flow of high temperature heating gases therethrough.

5. A steam generating and superheating system according to claim 4wherein an oxygen steel making furnace discharges hot gases into saidhood during a minor portion of a steel refining cycle.

6. A steam generating and superheating system according to claim 2wherein the steam produced by said power boiler is superheated, and saidsuperheated steam is combined with saturated steam from said accumulatorfor further heating in said superheating tubes.

7. A steam generating and superheating system according to claim 2wherein the rate of high heat value fuel burned in said furnace isregulated in accordance with a desired steam production in said powerboiler in cooperation with proportional gas flow through said parallelgas fiow sections.

8. A steam generating and superheating system according to claim 1wherein wall means define an elongated superheater housing to enclosesaid bank of steam superheating tubes, battle means in "said housingdirect a reversed series fiow of heating gases over said bank of steamsuperheating tubes, and the flow of mixed steam through said tubes iscountercurrent with respect to said heating gas flow.

9. A steam generating and superheating system according to claim 8wherein a row of tubes are extended along the roof and rear wall andthrough the floor of said superheater housing to receive steam from saidmixer means and to supply steam to said bank of superheater tubes.

References Cited UNITED STATES PATENTS 3,118,429 1/1964 Hochmuth l2273,217,695 11/1965 Durham 122-7 3,303,827 2/1967 Kemmetmuller et al. 1227KENNETH W. SPRAGUE, Primary Examiner.

1. A STEAM GENERATING AND SUPERHEATING SYSTEM INCLUDING A POWER BOILER,SAID POWER BOILER COMPRISING A FURNANCE, MEANS FOR BURNING HIGH HEATVALUE FUEL IN SAID FURNACE, A CONVECTION GAS-PASS DIVIDED INTO A PAIR OFPARALLEL GAS FLOW SECTIONS COMMUNICATING WITH SAID FURNACE, A BANK OFSTREAM GENERATING TUBES POSITIONED IN ONE OF SAID SECTIONS, A BANK OFSTEAM SUPERHEATING TUBES IN THE OTHER OF SAID SECTIONS, MEANS FORPROPORTIONING GAS FLOW FROM SAID FURNACE TO SAID PARALLEL GAS FLOWSECTIONS, A STEAM ACCUMULATOR, MIXER MEANS FOR COMBINING A FLOW OFSATURATED STEAM FROM SAID ACCUMULATOR AND STEAM FROM SAID STEAMGENERATOR FOR DELIVERY OF THE MIXTURE TO SAID SUPERHEATER TUBES, ANDMEANS RESPONSIVE TO THE TEMPERATURE OF THE MIXED SUPERHEATED STEAMLEAVING SAID SUPERHEATER TUBES TO PROPORTION GAS FLOW THROUGH SAIDPARALLEL GAS FLOW SECTIONS.